This invention relates to a stereo broadcast receiver and more particularly, to a receiver for use in four-channel stereo broadcasting.
Recently, there have been proposed many types of systems for quadraphonic FM broadcasting. It is usual that a frequency-modulated composite signal is transmitted from one broadcasting station in these systems. The composite signal generally includes a main channel component, first and second sub-channel components and at least one pilot signal to transmit quadraphonic signals i.e. a left front phonic signal (LF), a left back signal (LB), a right front signal (RF) and a right back signal (RB).
For example, the main channel component comprises the main channel signal (LF + LB) + (RF + RB) for reproduction of quadraphonic signals. Further, the first sub-channel component includes the first sub-channel signal (LF + LB) - (RF + RB) and the second sub-channel signal (LF - LB) + (RF - RB). Moreover, the second sub-channel component has the third sub-channel signal represented by (LF - LB) - (RF - RB).
Therefore, to reproduce quadraphonic signals, the receiver should be provided with an FM tuner for discriminating the composite signal, a demodulator for deriving each channel and a de-matrix circuit for separating the derived demodulated into quadraphonic signals.
Further, the demodulator responsive to any discriminated outputs from the FM tuner is usually equipped with three switching circuits. The composite signal through the FM tuner is, therefore, sampled at each of three switching circuits by each sampling pulse series produced from the pilot signal.
However, the FM tuner is not uniform in delay characteristic over the whole frequency band of the composite signal. Especially, the second sub-channel component is subject to large delay by the FM tuner as compared with the remaining channel components.
There has also been proposed a receiver system wherein the second sub-channel component of a single side band is derived through a band-pass filter. In this proposed receiver system, the difference in delay between the second sub-channel component and the remaining components occurs by the band-pass filter.
It is an object of this invention to provide a demodulator for use in quadraphonic FM broadcasting which enables the removal of any phase difference between each of the channel components.
It is a further object of this invention to provide a demodulator suitable for four-channel stereo use, wherein the main and the first sub-channel components are equalized so as to be equal in delay time to the second sub-channel component.
It is a still further object of this invention to provide a delay circuit which provides delay equalization and sampling of the composite signal, simultaneously.
It is a further object of this invention to provide a logic circuit in such a demodulator which is responsive to outputs of the delay circuit for deriving the main and first sub-channel components.